1. Field of the Invention
The present invention generally relates to a gas lift plunger assembly for use in a gas-producing well and, more particularly, is concerned with pad plunger assembly with a pad subassembly having a concave exterior configuration.
2. Description of the Prior Art
Gas-producing wells typically employ a plunger disposed within tubing of the well and capable of traveling vertically in the tubing as the well is cycled between shut-in and opened conditions in a manner well-known to one of ordinary skill in the art. The plunger is freely movable vertically in the well tubing and is adapted to rise vertically under the force of sufficient gas pressure to drive or lift the plunger and a slug of liquid, such as oil, above it to the surface while isolating the base of the liquid slug from the gas which lifts the plunger. The plunger falls by gravity back down the tubing of the well after the slug of liquid has been delivered to the surface and the gas pressure in the well tubing has decreased due to the transmission of gas from the well tubing to a suitable storage location.
One prior art plunger assembly, being shown in FIG. 1 and called a pad plunger 10, has an elongated rigid non-flexible central rod or mandrel 12 and a pair of end members 14, 16 attached to the opposite ends 12A, 12B of the mandrel 12. Between the opposite ends 12A, 12B of the mandrel 12, the plunger 10 also includes one or more subassemblies 18 of three spring-loaded interlocking pad sections 20 which surround the mandrel 12. The spring-loaded pad subassembly 18 can expand outwardly from and contract inwardly toward the mandrel 12 to compensate for any irregularities in the tubing T. The pad sections 20 of the pad subassembly 18 together form a generally cylindrical exterior surface 22 which creates a moving frictional seal with the interior wall W of the well tubing T.
The conventional view, which it now turns out is a common misconception, is that the longer the pad subassembly of the plunger the more sealing surface provided against the tubing wall and the better the frictional seal formed between the pad plunger and the tubing. Given the cylindrical shape of the exterior surface of the prior art pad subassembly, the more correct view now appears to be the longer the pad subassembly the more friction generated and the less efficiently the plunger runs through the well tubing.
Consequently, a need still exists for an innovation which provides a solution to the aforementioned problem in the prior art without introducing any new problems in place thereof.
The present invention provides a pad plunger assembly with a pad subassembly having a concave exterior configuration designed to satisfy the aforementioned need. The solution of the present invention to the aforementioned problem is to provide a pad plunger assembly whose pad sections together provide an exterior surface of a concave configuration which minimizes friction on the tubing wall so as to assist the plunger in running more efficiently through the tubing. Such concave configuration solves the aforementioned problem raised by the cylindrical configuration of the prior art pad subassembly.
Accordingly, the present invention is directed to a pad plunger assembly for use in gas well tubing. The pad plunger assembly comprises: (a) an elongated mandrel having opposite ends and a longitudinal axis extending between the opposite ends; (b) a pair of opposite end members each attached to one of the opposite ends of the mandrel; and (c) at least one seal-forming pad subassembly disposed about the mandrel and between the opposite end members thereon, the pad subassembly having an outer exterior surface of an annular concave configuration formed by opposite end portions of the outer exterior surface being disposed farther radially outwardly from the longitudinal axis of the mandrel than an intermediate portion of the outer exterior surface is disposed radially outwardly from the longitudinal axis of the mandrel such that a frictional seal is provided on the interior wall surface of the gas well tubing by the opposite end portions of the outer exterior surface of the pad subassembly which creates less friction than would be created by an outer exterior surface of cylindrical configuration on the pad subassembly.
More particularly, the mandrel is a rigid non-flexible solid rod. The end members and the opposite ends of the mandrel have fastening elements, such as complementary internal and external threads, permitting the end members to be removably fastened, namely threadably attached, to the opposite ends of the mandrel.
Further, a volume is defined between the interior wall surface of the gas well tubing and the intermediate portion of the outer exterior surface of the pad subassembly which traps plunger lifting gas and thereby further enhances the frictional seal between the pad subassembly and the interior wall surface of the gas well tubing.
Still further, the seal-forming pad subassembly includes a plurality of interlocking pad sections disposed about the mandrel and between the opposite end members thereon. The pad sections have coil springs between the pad sections and the mandrel, thereby spring-loading and thus biasing the pad sections to move radially outward from the mandrel such that the pad subassembly can expand outwardly from and contract inwardly toward the mandrel. Each of the pad sections has an outer exterior surface segments of a concave configuration which together form the outer exterior surface of the seal-forming pad subassembly.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.